getImplementationHints

Map of hints (maybe unmodifiable) used by
this factory to customize its use. This map is not guaranteed to contains
all the hints supplied by the user; it may be only a subset. Consequently, hints provided
here are usually not suitable for creating new factories, unless the implementation make some
additional garantees (e.g. FactoryUsingVolatileDependencies).

The primary purpose of this method is to determine if an existing factory
instance can be reused for a set of user-supplied hints. This method is invoked by FactoryRegistry in order to compare this factory's hints against user's hints. This is
dependency introspection only; FactoryRegistrynever invokes this
method for creating new factories.

Keys are usually static constants from the Hints class, while values are instances
of some key-dependent class. The key set must contains at least all
hints impacting functionality. While the key set may contains all hints supplied by the user,
it is recommended to limit the set to only the hints used by this particular factory
instance. A minimal set will helps FactoryRegistry to compare only hints that matter
and avoid the creation of unnecessary instances of this factory.

The hint values may be different than the one supplied by the user. If a user supplied a
hint as a Class object, this method shall replace it by the actual instance used, if
possible.

Implementations of this method are usually quite simple. For example if a datum authority factory uses an ordinary
datum factory, its method could be
implemented as below (note that we should not check if the datum factory is null, since key
with null value is the expected behaviour in this case). Example: